Evolution and Signatures Evolution and Signatures of of Helical Magnetic Fields Helical Magnetic Fields Tina Kahniashvili Tina Kahniashvili McWilliams Center for Cosmology McWilliams Center for Cosmology Carnegie Mellon University Carnegie Mellon University & Abastumani Astrophysical Observatory Abastumani Astrophysical Observatory Ilia State University Ilia State University NORDITA NORDITA June 24 2015 June 24 2015
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Evolution and Signatures of Helical Magnetic Fields Tina Kahniashvili McWilliams Center for Cosmology Carnegie Mellon University & Abastumani Astrophysical.
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Evolution and SignaturesEvolution and Signaturesofof
Helical Magnetic Fields Helical Magnetic Fields
Tina KahniashviliTina Kahniashvili
McWilliams Center for CosmologyMcWilliams Center for CosmologyCarnegie Mellon UniversityCarnegie Mellon University
Pogosian, Vachaspati, and Winitski 2000, Caprini, Durrer, and Pogosian, Vachaspati, and Winitski 2000, Caprini, Durrer, and Kahniashvili, 2003, Kahniashvili and Ratra 2005, Kunze 2012, Kahniashvili, 2003, Kahniashvili and Ratra 2005, Kunze 2012, Kahniashvili, et al. 2014, Balardini, Finelli, and Paoletti, 2014Kahniashvili, et al. 2014, Balardini, Finelli, and Paoletti, 2014
Magnetic Helicity vs. WMAP 9 years Magnetic Helicity vs. WMAP 9 years datadata
If the magnetic field has been generated If the magnetic field has been generated through a causal process in the early through a causal process in the early universe ituniverse it’’s correlation length could not s correlation length could not exceed the Hubble horizon at the moment exceed the Hubble horizon at the moment of the generation of the generation
MHD Modeling
Coupling of the magnetic Coupling of the magnetic field with primordial field with primordial plasmaplasma
Injection of the magnetic Injection of the magnetic energy at a given scale energy at a given scale (phase transition bubble)(phase transition bubble)
Brandenburg, Kahniashvili, Tevzadze 2014
Modeling Magnetic FieldModeling Magnetic Field
smoothed vs. effective smoothed vs. effective magnetic fieldmagnetic field
one-scale (delta function)one-scale (delta function)magnetic field magnetic field
Kahniashvili, Tevzadze, Brandenburg, Neronov 2013
Non-helical fieldNon-helical field
Helical fieldHelical field• Helicity conservation law Helicity conservation law
"»M E3=2Ma2
Phase Transitions Generated Magnetic Field Phenomenology
Our analysis show that in the most optimistic scenario the magnetic correlation length in the comoving frame can reach 10 kpc with the amplitude of the effective magnetic field being 0.007 nG. We demonstrate that the considered model of magneto-genesis can provide the seed magnetic field for galaxies and clusters.
Magnetic Helicity GrowthTevzadze, Kisslinger, Brandenburg, Kahniashvili 2012
The correlation length The correlation length should satisfy: should satisfy:
Fractional magnetic Fractional magnetic helicity grows until it helicity grows until it reaches its maximal valuereaches its maximal value
Helical Magnetic Fields DecayHelical Magnetic Fields Decay
Brandenburg, Kahniashvili, Tevzadze 2015
Causal fields – correlation length limitationCausal fields – correlation length limitationnnBB=2 or n=2 or nBB=0=0
Inverse CascadeInverse Cascade
Helical Magnetic Fields Helical Magnetic Fields DecayDecay Vachaspati 2001Vachaspati 2001
Helical Magnetic FieldHelical Magnetic Field
Brandenburg, Kahniashvili, Tevzadze 2015
Inflationary Magnetic HelicityInflationary Magnetic Helicity
Magnetic field correlation length might be as large Magnetic field correlation length might be as large as the Hubble horizon today or even larger as the Hubble horizon today or even larger (infinity)(infinity)
Can we see the imprints of an a-causal field?Can we see the imprints of an a-causal field?
The absence of inverse cascade for Inflation generated magnetic fields
Helical Magnetic FieldsHelical Magnetic FieldsScaling LawsScaling Laws
Brandenburg, Kahniashvili, Tevzadze 2015
ConclusionConclusion
The lower bound of the extragalactic magnetic field The lower bound of the extragalactic magnetic field favorsfavors a primordial magnetogenesis approach (in a primordial magnetogenesis approach (in particular, helical magnetic fields)particular, helical magnetic fields)
The primordial magnetic field might be a plausible The primordial magnetic field might be a plausible explanation for the galaxy magnetic fieldexplanation for the galaxy magnetic field
Cosmological magnetic field order of 0.1 nanoGauss Cosmological magnetic field order of 0.1 nanoGauss can be detectable by the nearest future CMB can be detectable by the nearest future CMB polarization and LSS measurementspolarization and LSS measurements
On the other hand, if the field is significantly On the other hand, if the field is significantly smaller – it would satisfy the LOWER limit bound but smaller – it would satisfy the LOWER limit bound but would not been observable through cosmological would not been observable through cosmological observations observations